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  <div class="section" id="numpy-diff">
<h1>numpy.diff<a class="headerlink" href="#numpy-diff" title="Permalink to this headline">¶</a></h1>
<dl class="function">
<dt id="numpy.diff">
<code class="sig-prename descclassname">numpy.</code><code class="sig-name descname">diff</code><span class="sig-paren">(</span><em class="sig-param">a</em>, <em class="sig-param">n=1</em>, <em class="sig-param">axis=-1</em>, <em class="sig-param">prepend=&lt;no value&gt;</em>, <em class="sig-param">append=&lt;no value&gt;</em><span class="sig-paren">)</span><a class="reference external" href="https://github.com/numpy/numpy/blob/v1.18.1/numpy/lib/function_base.py#L1141-L1271"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#numpy.diff" title="Permalink to this definition">¶</a></dt>
<dd><p>Calculate the n-th discrete difference along the given axis.</p>
<p>The first difference is given by <code class="docutils literal notranslate"><span class="pre">out[i]</span> <span class="pre">=</span> <span class="pre">a[i+1]</span> <span class="pre">-</span> <span class="pre">a[i]</span></code> along
the given axis, higher differences are calculated by using <a class="reference internal" href="#numpy.diff" title="numpy.diff"><code class="xref py py-obj docutils literal notranslate"><span class="pre">diff</span></code></a>
recursively.</p>
<dl class="field-list">
<dt class="field-odd">Parameters</dt>
<dd class="field-odd"><dl>
<dt><strong>a</strong><span class="classifier">array_like</span></dt><dd><p>Input array</p>
</dd>
<dt><strong>n</strong><span class="classifier">int, optional</span></dt><dd><p>The number of times values are differenced. If zero, the input
is returned as-is.</p>
</dd>
<dt><strong>axis</strong><span class="classifier">int, optional</span></dt><dd><p>The axis along which the difference is taken, default is the
last axis.</p>
</dd>
<dt><strong>prepend, append</strong><span class="classifier">array_like, optional</span></dt><dd><p>Values to prepend or append to <em class="xref py py-obj">a</em> along axis prior to
performing the difference.  Scalar values are expanded to
arrays with length 1 in the direction of axis and the shape
of the input array in along all other axes.  Otherwise the
dimension and shape must match <em class="xref py py-obj">a</em> except along axis.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 1.16.0.</span></p>
</div>
</dd>
</dl>
</dd>
<dt class="field-even">Returns</dt>
<dd class="field-even"><dl class="simple">
<dt><strong>diff</strong><span class="classifier">ndarray</span></dt><dd><p>The n-th differences. The shape of the output is the same as <em class="xref py py-obj">a</em>
except along <em class="xref py py-obj">axis</em> where the dimension is smaller by <em class="xref py py-obj">n</em>. The
type of the output is the same as the type of the difference
between any two elements of <em class="xref py py-obj">a</em>. This is the same as the type of
<em class="xref py py-obj">a</em> in most cases. A notable exception is <code class="xref py py-obj docutils literal notranslate"><span class="pre">datetime64</span></code>, which
results in a <code class="xref py py-obj docutils literal notranslate"><span class="pre">timedelta64</span></code> output array.</p>
</dd>
</dl>
</dd>
</dl>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p><a class="reference internal" href="numpy.gradient.html#numpy.gradient" title="numpy.gradient"><code class="xref py py-obj docutils literal notranslate"><span class="pre">gradient</span></code></a>, <a class="reference internal" href="numpy.ediff1d.html#numpy.ediff1d" title="numpy.ediff1d"><code class="xref py py-obj docutils literal notranslate"><span class="pre">ediff1d</span></code></a>, <a class="reference internal" href="numpy.cumsum.html#numpy.cumsum" title="numpy.cumsum"><code class="xref py py-obj docutils literal notranslate"><span class="pre">cumsum</span></code></a></p>
</div>
<p class="rubric">Notes</p>
<p>Type is preserved for boolean arrays, so the result will contain
<em class="xref py py-obj">False</em> when consecutive elements are the same and <em class="xref py py-obj">True</em> when they
differ.</p>
<p>For unsigned integer arrays, the results will also be unsigned. This
should not be surprising, as the result is consistent with
calculating the difference directly:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">u8_arr</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">],</span> <span class="n">dtype</span><span class="o">=</span><span class="n">np</span><span class="o">.</span><span class="n">uint8</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">np</span><span class="o">.</span><span class="n">diff</span><span class="p">(</span><span class="n">u8_arr</span><span class="p">)</span>
<span class="go">array([255], dtype=uint8)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">u8_arr</span><span class="p">[</span><span class="mi">1</span><span class="p">,</span><span class="o">...</span><span class="p">]</span> <span class="o">-</span> <span class="n">u8_arr</span><span class="p">[</span><span class="mi">0</span><span class="p">,</span><span class="o">...</span><span class="p">]</span>
<span class="go">255</span>
</pre></div>
</div>
<p>If this is not desirable, then the array should be cast to a larger
integer type first:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">i16_arr</span> <span class="o">=</span> <span class="n">u8_arr</span><span class="o">.</span><span class="n">astype</span><span class="p">(</span><span class="n">np</span><span class="o">.</span><span class="n">int16</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">np</span><span class="o">.</span><span class="n">diff</span><span class="p">(</span><span class="n">i16_arr</span><span class="p">)</span>
<span class="go">array([-1], dtype=int16)</span>
</pre></div>
</div>
<p class="rubric">Examples</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">x</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">0</span><span class="p">])</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">np</span><span class="o">.</span><span class="n">diff</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
<span class="go">array([ 1,  2,  3, -7])</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">np</span><span class="o">.</span><span class="n">diff</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">n</span><span class="o">=</span><span class="mi">2</span><span class="p">)</span>
<span class="go">array([  1,   1, -10])</span>
</pre></div>
</div>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">x</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">array</span><span class="p">([[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">10</span><span class="p">],</span> <span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">8</span><span class="p">]])</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">np</span><span class="o">.</span><span class="n">diff</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
<span class="go">array([[2, 3, 4],</span>
<span class="go">       [5, 1, 2]])</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">np</span><span class="o">.</span><span class="n">diff</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">axis</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
<span class="go">array([[-1,  2,  0, -2]])</span>
</pre></div>
</div>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">x</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">arange</span><span class="p">(</span><span class="s1">&#39;1066-10-13&#39;</span><span class="p">,</span> <span class="s1">&#39;1066-10-16&#39;</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="n">np</span><span class="o">.</span><span class="n">datetime64</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">np</span><span class="o">.</span><span class="n">diff</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
<span class="go">array([1, 1], dtype=&#39;timedelta64[D]&#39;)</span>
</pre></div>
</div>
</dd></dl>

</div>


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